Conversion from alt_json to json produces incorrect result

[falbrechtskirchinger]

A proposed unit test for unit-alt-string.cpp contained the following code:

        alt_json j = R"(
        {
            "foo": ["bar", "baz"]
        }
        )"_json;

This conversion compiles but fails to produce the expected result. Instead, the resulting object is in fact the following array:

[[[102,111,111],[[98,97,114],[98,97,122]]]]

The test can be further reduced to this:

alt_json j = json::object();

Resulting in:

[]

The cause is the incorrect selection of this to_json() function for CompatibleArrayType = std::map<...>.

template < typename BasicJsonType, typename CompatibleArrayType,
           enable_if_t < is_compatible_array_type<BasicJsonType,
                         CompatibleArrayType>::value&&
                         !is_compatible_object_type<BasicJsonType, CompatibleArrayType>::value&&
                         !is_compatible_string_type<BasicJsonType, CompatibleArrayType>::value&&
                         !std::is_same<typename BasicJsonType::binary_t, CompatibleArrayType>::value&&
                         !is_basic_json<CompatibleArrayType>::value,
                         int > = 0 >
void to_json(BasicJsonType& j, const CompatibleArrayType& arr)
{
    external_constructor<value_t::array>::construct(j, arr);
}

I suspect an error in is_constructible_object_type and will investigate.

The requirements placed on object_t, string_t, etc. should be clearly documented. Maybe a trait like is_sax would help?